1. Field of the Invention
The present invention relates to a method for determining whether a maintenance message indicating a fault in a system is or is not representative of a real fault in said system, as well as a device for implementing this method.
2. Background Art
It is known that, in very varied fields of activity, such as, for example, in industry, motoring or aviation, there exist centralized maintenance devices associated with systems which are designed and intended to assist maintenance operations for returning said systems to operational condition, at the end of an operating cycle. In the context of the present invention, operating cycle is understood to be a defined operating duration of the associated system and characterized by at least partial shutting-down of said system, at the end of a cycle, in order to carry out the necessary maintenance operations. By way of example, it may relate to a flight for an aircraft or of a constant defined duration, for example the duration of an item of work, for a machine in industry.
One of the main functions of a centralized maintenance device is to supply a maintenance report on the operation carried out, at the end of an operating cycle. This maintenance report consists of a list of maintenance messages, each of said maintenance messages identifying at least one element of the system, which is faulty and which therefore has to be replaced.
By reason of the generally high number of elements monitored and of the complexity of the systems in question, the list of maintenance messages often comprises a certain number of spurious messages. A message is considered as spurious, in the context of the present invention, when it is not representative of any real fault in the system.
The object of the present invention is thus to determine whether a maintenance message generated is representative of a real fault in the system or whether this message is spurious.
Hence, although the present invention is applicable to various systems, it will be described more particularly below in the context of an aircraft, the operation of which is monitored by a centralized maintenance device.
It will be noted that, in the case of an aircraft, many elements are generally replaced although no fault exists. The cost of such unjustified removals, over the duration of use of an aircraft, may be evaluated at about 5 to 10% of the purchase price of the aircraft.
Thus, considerable efforts are made to eliminate spurious maintenance messages. They consist mainly in understanding the causes of these spurious messages by seeking to identify the imperfections in the models used in the fault detection and then to correct these models. In the case of an aircraft, such corrections make it possible to pass from a few tens of spurious maintenance messages (out of several thousands of possible messages) to a few spurious messages per flight.
However, the identification and thus the correction of the imperfections in the models used are often limited by the impossibility of reproducing certain phenomena in the laboratory. In certain cases, the solution would require the introduction of new parameters which are not available in the system used and thus of major and extremely costly modifications of the system.
So as further to reduce the spurious messages, one recommended solution consists, by passive filtering, in definitively eliminating these spurious messages from the maintenance report. This solution exhibits numerous drawbacks, in particular:
the operator tasked with the maintenance no longer has information in the maintenance report when real faults appear in elements, from which the associated maintenance message has been eliminated; PA0 the list of spurious messages to be eliminated must be manually updated when new cases arise; and PA0 as all the messages may, a priori, be spurious one day, the list of the messages to be eliminated never stops growing, and thus the maintenance report rapidly risks losing any benefit. PA0 a long-term occurrence rate of said maintenance message is determined, on the basis of the results of a number N of preceding cycles, the occurrence rate corresponding to the average probability of occurrence, that is to say of generation, of said maintenance message in the course of a cycle; PA0 a short-term occurrence rate of said maintenance message is determined, at the most on the basis of the results of the last N cycles; PA0 said short-term occurrence rate is compared with said long-term occurrence rate; and PA0 it is deduced therefrom: PA0 a computer (CAL) linked to said set of memories, calculating, at the end of a cycle, for each maintenance message generated in the course of this cycle, the long-term and short-term occurrence rates of said maintenance message on the basis of the information recorded in said set of memories; and PA0 a comparator linked to said computer, comparing the calculated short-term occurrence rate to the calculated long-term occurrence rate for each maintenance message generated, determining whether the message considered is spurious or not, and communicating this result.
According to a later solution used, manual tests for fault confirmation are carried out by the maintenance operators so as to identify the remaining spurious messages. The drawbacks of these manual tests are many.
In particular, said tests entail time being wasted, and sometimes even delays in the departure of the aircraft, when they are numerous and have to be repeated frequently.